The application, "Extrinsic Factors Influending Myocardial Performance," proposes three separate canine studies. Part I: To determine the time course of activation of contractile elements of the left ventricle (LV) in terms of myocardial oxygen consumption (MVO2), force development, and the rate of change of activation with volume changes. Studies will be conducted in an isolated supported heart using a hydraulic servo-system and microcomputer which allow large volumes to be ejected from the LV rapidly (1 ml/ms) during systole. These experiments will provide data for a more robust model for predicting MVO2 in patients with ischemic heart disease in which accurate measurement of oxygen demand is critical. Part II: To test the hypothesis that improvements in LV performance as end-diastolic volume, i.e. muscle length, is increased become more efficient in terms of MVO2 as the inotropic state is depressed. The experimental model will be the same isolated supported heart using a hydraulic servo-system and microcomputer as used in Part I. However ejections will be programmed within the physiologic range. Two examples of myocardial depressants will be studied: halothane and decreased ionized calcium, agents which appear to affect calcium transport differently. These studies will provide specific data for predicting myocardial MVO2 for patients undergoing anesthesia with halothane, or experiencing hypocalcemia which often occurs during such conditions as cardiopulmonary bypass, massive blood transfusion, and hemorrhagic pancreatitis. These data will provide insights into changes in LV efficiency and in MVO2 caused by direct myocardial depressants used in patients. Part III: To characterize end-systolic relationships of LV pressure and regional wall stress to regional dimensions and to use these relationships to study function of the normally perfused LV posterior wall during LV shape changes, elicited by first lengthening and anterior wall segment by ischemia and then shortening it surgically. Sonomicrometers, auxotonic force gauges, and two-dimensional echocardiography will be used in the right heart bypass model to test the hyposthesis that depressed performance in the normal segment is caused by increased wall stress related to length changes in the ischemic segment. The data will improve the understanding of mechanisms of interactions between LV regions and of LV reginal function in patients with acute myocardial ischemia, infarcts, and LV aneurysms.